As is well-known, tower cranes are used in constructing buildings. Some are free-standing, but the types of tower cranes to which this invention relates are generally positioned within the building under construction, supported by the building structure, usually passing through aligned floor slab openings created for this purpose. The tower of the tower crane is usually supported from one floor, extending upward through aligned openings in all completed upper floors. As construction of the building progresses and the floors approach the boom of the crane, the tower, crane and boom must be raised or “jumped” to a higher elevation.
For jumping the tower, one system previously in common use employed a hydraulic cylinder connected to a specially equipped lower mast section, with an additional cross piece connected to the cylinder and engaged in a pair of opposed ladder-like columns extending from the lower floors to the top of the building alongside the tower, within the shaft of floor openings. Dogs of this lifting structure would engage on rungs or slots of these ladder devices, moving up the ladders and engaging new slots as the lifting cylinder was actuated. Since the ladder devices extended through the entire height of the building, they served as supporting means for the working crane, as well as being involved in the lifting operation when raising of the crane was required.
In another lifting system which has been widely used, jacks were positioned on a floor of the building structure, with smooth lifting rods depending downwardly from the jacks to a connecting device engagable with a specially equipped mast section. A device associated with the jacks and having teeth would grasp each rod for the lifting stroke. The specially equipped mast section, normally located at the bottom of the tower crane, had holes for receiving the connecting device, which extended laterally through the mast. The tower crane was supported entirely by the rods and connecting device while being lifted by a series of jacking strokes.
For supporting the crane after it was lifted to the new elevation, this latter system utilized I-beams inserted horizontally through a mast section. The jacks lowered the crane a short distance, to rest the I-beam on a building floor.
For these prior lifting systems, it is important to provide not only suppport for the vertical load of the tower crane, but also for the lateral load or side loading to prevent the crane from tipping and to accept twisting forces induced by the boom.
Initially when no floors have been erected, a relatively deep foundation and long support rods that tie the tower to the foundation are provided to prevent the side loading or turning moment of the boom from toppling the crane. As floors are added, the vertical and lateral loads are distributed to either the floors or the horizontal beams or both. These loads are greater than the floors and horizontal beams would normally experience after construction, and the floors and horizontal beams are therefore specially reinforced and shored to accept these additional loads that the tower crane imparts. Moreover, the bay of a building under construction is usually larger than the cross sectional area of a tower supporting the crane. Consequently, the floor space of the bay, as each floor is added, is filled around the tower with little clearance solely to accommodate the crane. The filled floor space is also generally reinforced. To provide further lateral support, chucking such as braces, wedges or plates are also provided over the floors around the opening for the tower.
As persons of ordinary skill in the art can appreciate, however, these added features involve a substantial amount of additional construction materials and labor solely to accommodate the tower crane. As a result, construction cost increases substantially and the added space of the extra construction materials reduces the usable space of the building. Moreover, conventional crane lifting systems are cumbersome to operate, often requiring an entire day or more to jump the crane, resulting in substantial construction down time.
Therefore, there is a need to provide an improved tower crane lifting device in which the crane load is not distributed to the horizontal beams and the lifting can be performed relatively rapidly with minimum down time.